The present invention is directed to dot impact matrix printers in which the printing operation is performed by a plurality of elongated printing rods or wires each having a free end which is aligned in a vertical row in a small concentrated area adjacent the printing medium. Most commonly, the impact dot matrix-type printers produce characters by matrices of 5.times.7, 7.times.7 or 9.times.7 dots with additional or half step dots sometimes also being added. The dots are formed by a print head which includes a solenoid or an electromagnetic actuator which is selectively activated to drive the printing wires a very short distance to impact the printing medium. Usually only a single vertical row of seven print wire ends is carried by the print head while in some instances a double vertical row of print wires is provided. As the print head traverses the page, the actuators are selectively "fired" on a time basis so that the dots are printed, usually on-the-fly. In addition to the thirty-five positions or cross lines of a 5.times.7 matrix, dots are often printed between the cross lines at so-called half steps to produce a better defined character.
The present invention also relates to dot matrix printers of the page type in which a large number, e.g., forty-four to one hundred and thirty-two, of print heads extend across the page so that all or nearly all of the print heads may be actuated simultaneously to print a line of dots almost simultaneously. Then, the paper is moved in a vertical direction relative to the print wire ends to print the next line of dots. This cycle is repeated until the full matrix has been scanned and the printed line completed.
The solenoids and magnets which drive the print wires have been arranged in various fashions, such as a circular arrangement of the actuators, such as shown in U.S. Pat. Nos. 3,842,955 and 3,854,564. As disclosed in these patents, there is an attempt to concentrate the actuators for the print wires in a small, closed circle. In the more conventional and earlier developments of dot impact matrix printers, the print heads carried long, bowed wires fanning out a large array of electromagnetic actuators. The actuators require considerably more space than the small concentrated vertical row of wire tip ends. Typical of these types of curved wires are shown and disclosed in U.S. Pat. Nos. 3,690,431 and 3,882,986. In still further instances, a solenoid type construction is used with the print wire being attached to the movable solenoid core and such is shown in U.S. Pat. Nos. 3,797,629; 3,892,175; and 3,729,079.
The present invention is also directed to electromagnetic actuators of the kind, sometimes referred to as the clapper type, such as has been described in U.S. Pat. No. 3,828,508. In this patent, a circular arrangement of clapper types of actuators is disclosed as an attempt to simplify the construction for the printing head. A still further disclosure of a print head actuator of a simplified construction, but using a torsion spring actuator, is disclosed in U.S. Pat. No. 3,982,622.
The problems due to friction when using long bowed print wires, as well as the inertia for moving the long print wires and their actuators, are well known. Likewise, the mass and the size of the print heads result in inertia problems and the use of many parts therein raises the cost of the printing head.
Thus, there is a need for a lightweight, compact and inexpensive print head which is easy to assemble and which uses substantially straight print wires. In this invention, the wire actuators are assembled of elements which perform multiple functions and which can be readily assembled without the use of the typical pin hinges, separate springs and other adjustment elements, thereby resulting in a new and improved actuator having general utility for various types of dot matrix printers.